The subject matter disclosed herein relates to an optical sensor used in a safety system and, more specifically, to an optical sensor including a dual array of photosensitive devices providing redundant frames.
An optical sensor includes a receiver that converts light incident to the sensor into an electric signal. The receiver may include a single photosensitive device or an array of pixels, for example charge-coupled devices (CCD), complementary metal-oxide-semiconductor (CMOS) sensors, or time-of-flight (TOF) sensors. Each pixel converts the light incident to that pixel to a separate electrical signal. The optical sensor typically has an opening through which the light passes and may further include a lens or optical filter over the opening to focus the light on the detector. Depending on the application requirements and the configuration of the sensor, the optical sensor is suited for a variety of uses ranging from indicating the presence of a beam of light to reproducing a three dimensional (3D) image of an object.
It is known that optical sensors may be a component of a safety system, such as a light curtain or a 3D camera monitoring access to or operation of an industrial machine or process line. The optical sensor, in cooperation with a corresponding optical source, may be used to protect an operator from a potentially hazardous operating region or condition. For example, the optical source may transmit a light beam in front of the restricted region and the optical sensor detects a person or object entering the region via discontinuous reception of the beam. Alternately, the optical sensor may reproduce an image of an object passing through the emitted light. The light beam or the image may be used to determine whether an undesired object or a person has entered a restricted region and appropriate action, such as shutting down a portion or all of the equipment within the region may result.
It is further known that optical sensors are subject to certain failures. For example, adjacent pixels or selection lines to enable a pixel may become shorted together. Further, pixels may not return to a fully discharged state during a reset. When the optical sensor is used within a safety system, it is desirable to detect any failures of the sensor such that the safety of an operator is not compromised. Further, it is desirable to promptly detect the failure to prevent unsafe operation for a period of time, for example, until a scheduled maintenance interval.
Thus, it would be desirable to provide an optical sensor that continually monitors its performance without interrupting normal operation of the sensor.